The present disclosure relates to a fixing device fixing a toner image onto a recording medium and an image forming apparatus including the fixing device.
Conventionally, an electrographic image forming apparatus, such as a printer or a copying machine, forms a toner image onto a surface of a recording medium, such as a sheet, and then, heats and pressures the recording medium and toner image by a fixing device, thereby fixing the toner image onto the recording medium.
Recently, because requests of energy saving and shortening of a warm-up time are increased, reduction of a heat capacity of the fixing device is actively considered. As a concrete manner actualizing the reduction of a heat capacity of the fixing device, for example, there is a “slide belt manner”. The fixing device with the slide belt manner includes a flexible fixing belt, a pressuring member coming into pressure contact with the fixing belt to form a fixing nip and a pressing member pressing the fixing belt toward a side of the pressuring member. Generally, when the pressuring member is rotated by a drive source connected to the pressuring member, the fixing belt is co-rotated with the rotation of the pressuring member and the fixing belt is slid with respect to the pressing member.
In the fixing device with the slide belt manner, when the operation fixing the toner image onto the recording medium is repeated, the pressing member is worn at a part of the pressing member coming into slide contact with the fixing belt and a sliding load of the fixing belt (a load required for sliding the fixing belt with respect to the pressing member) is increased. In addition, a surface of the fixing belt and a surface of the pressuring member are also deteriorated and drive force of the fixing belt (a co-rotational property of the fixing belt with respect to the pressuring member) is decreased. If these factors cause a slip between the pressuring member and fixing belt, it is impossible to co-rotate the fixing belt with rotation of the pressuring member, and therefore, there is a possibility that a part of the fixing belt is locally heated by a heat source. If such a situation occurs, there is a possibility that temperature of the part of the fixing belt is rapidly raised and the fixing belt is deformed.
A fixing device including a rotation detecting part detecting a rotation state of the fixing belt to prevent such a failure is disclosed. In such a conventional technique, a roller of the rotation detecting part comes into contact with an outer circumference face of the fixing belt. The roller is rotated simultaneously with the rotation of the fixing belt, and accordingly, the rotation state of the fixing belt may be detected.
However, in the above-mentioned conventional technique, in a case where paper dust, a toner and others are adhered onto the outer circumference face of the fixing belt or the roller or a case where a lubricant applied onto an inner circumference face of the fixing belt is spread to the outer circumference face of the fixing belt, a slip between the fixing belt and roller is caused, and then, it is difficult to surely detect the rotation state of the fixing belt by the rotation detecting part.
In the above-mentioned conventional technique, because the roller comes into contact with the outer circumference face of the fixing belt, there is a possibility that stress concentrates on a contact portion of the outer circumference face of the fixing belt and roller, and then, durability of the fixing belt is deteriorated.